[xml] xmlHashCreate and xmlHashAddEntry - hashs of unknown size?

Suppose I have a hash table who's size I do not know at compile time - it
might end up with one entry or a thousand.
What value should I pass to xmlHashCreate for the size?
If I pass a value "N", and at run time try to add "N+1" items to the hash,
will it error or will it just increase the hash size?